1. Field of the Invention
The present invention relates to a vacuum cast molding apparatus for defoaming, mixing, agitating and injecting molding materials into a die under vacuum.
2. Description of the Prior Art
A vacuum cast molding process is performed to make duplicated resin products of a master model. The process comprises the steps of making a die of the master model of silicon rubber, injecting (or pouring) liquid resin such as mixed polyurethane liquid into the silicon die, and solidifying it therein. Conventionally, vacuum cast molding apparatuses, which can be used to mix and agitate liquid resin and inject the resin into the silicon die under vacuum, have been used in the cast molding work.
In the conventional type of vacuum cast molding apparatuses, however, the size of the vacuum chamber in each cast molding apparatus, in which a silicon die is placed, cannot be changed. Therefore, several sizes of cast molding apparatus must be built according to sizes of cast molding products to be produced.
In the type of cast molding process as described above, operations of devices in a vacuum chamber such as a mixing and injecting device are controlled by an operator by operating the operator panel. Cast molding operations in the vacuum chamber can be observed through a viewing window provided on an external wall of the vacuum chamber. The operator operates the operator panel appropriately while observing the molding operations in the vacuum chamber.
However, in this type of vacuum cast molding apparatus, the position of the operator panel may often be remote from that of the viewing window. Therefore, the operator must move between the operator panel and the viewing window during the molding operation, which is troublesome.
The viewing window is made of a glass plate. Since the external surface of the glass plate is directly exposed to the outside of the vacuum chamber, the glass plate might be broken as a result of an impact thereon from outside. If the glass plate is broken under vacuum, the broken glass pieces are sucked into the vacuum chamber by external atmospheric pressure and collide against internal walls of the vacuum chamber, and then spurt out through an opening for the viewing window to outside.
The vacuum chamber is divided to an upper portion and a lower portion, each communicating with each other. The mixing and injecting device is installed in the upper portion and the silicon die is installed in the lower portion. Liquid molding materials mixed and agitated in the mixing and injecting device are injected or poured into the silicon die through a funnel. A lower edge port of the funnel is connected via a vinyl hose to a injection port formed in a silicon die, so that the molding materials smoothly flow into the silicon die.
The vinyl hose connecting the lower edge port of the funnel to the injection port of the silicon die is discarded and exchanged with a new one each time after cast molding work is carried out. When removing the old (or used) vinyl hose, if an operator bends the vinyl hose and faces the upper opening downward, molding materials remaining inside the hose may be spilled therefrom and contaminate inside of the vacuum chamber. In addition, when attaching a new hose, the hose may be bent unnecessarily, which may prevent molding materials from flowing smoothly into the die.
In cast molding operation using this type of vacuum cast molding apparatus, bubbles are always generated in molding materials when the materials are agitated. Therefore, the materials cannot flow into a die smoothly. In addition, in a die having a complicated internal configuration, it is difficult to spread molding materials to every internal corner space of the die even under vacuum.